U.S. patent application number 12/127638 was filed with the patent office on 2009-02-12 for zoom lens and image pickup apparatus including the same.
This patent application is currently assigned to CANON KABUSHIKI KAISHA. Invention is credited to Rei Iwama.
Application Number | 20090040622 12/127638 |
Document ID | / |
Family ID | 40106526 |
Filed Date | 2009-02-12 |
United States Patent
Application |
20090040622 |
Kind Code |
A1 |
Iwama; Rei |
February 12, 2009 |
ZOOM LENS AND IMAGE PICKUP APPARATUS INCLUDING THE SAME
Abstract
A zoom lens includes a first lens unit having a positive
refractive power, a second lens unit having a negative refractive
power, a third lens unit having a positive refractive power, and a
fourth lens unit having a positive refractive power in that order
from an object side to an image side. Zooming is performed by
changing distances between the lens units. The first lens unit
includes two or less lenses and the second lens unit consists of a
negative lens and a positive lens in that order from the object
side to the image side. The zoom lens satisfies the following
condition: -1.3<m1/ {square root over ((fwfT))}<-0.8 where fw
and fT are focal lengths of the entire lens unit at wide-angle and
telephoto ends, respectively, and m1 is an amount of movement of
the first lens unit in an optical axis direction during zooming
from the wide-angle end to the telephoto end.
Inventors: |
Iwama; Rei; (Utsunomiya-shi,
JP) |
Correspondence
Address: |
CANON U.S.A. INC. INTELLECTUAL PROPERTY DIVISION
15975 ALTON PARKWAY
IRVINE
CA
92618-3731
US
|
Assignee: |
CANON KABUSHIKI KAISHA
Tokyo
JP
|
Family ID: |
40106526 |
Appl. No.: |
12/127638 |
Filed: |
May 27, 2008 |
Current U.S.
Class: |
359/687 ;
359/684 |
Current CPC
Class: |
G02B 15/173 20130101;
G02B 15/144113 20190801 |
Class at
Publication: |
359/687 ;
359/684 |
International
Class: |
G02B 15/16 20060101
G02B015/16 |
Foreign Application Data
Date |
Code |
Application Number |
May 28, 2007 |
JP |
2007-140256 |
Claims
1. A zoom lens comprising: a first lens unit having a positive
refractive power; a second lens unit having a negative refractive
power; a third lens unit having a positive refractive power; and a
fourth lens unit having a positive refractive power, wherein the
first lens unit, the second lens unit, the third lens unit, and the
fourth lens unit are arranged in that order from an object side to
an image side, wherein the zoom lens performs zooming by changing
distances between the lens units, wherein the first lens unit
includes two or less lenses and the second lens unit consists of a
negative lens and a positive lens in that order from the object
side to the image side, and wherein the following condition is
satisfied: -1.3<m1/ {square root over ((fwfT))}<-0.8 where fw
and fT are focal lengths of the entire zoom lens at a wide-angle
end and a telephoto end, respectively, and m1 is an amount of
movement of the first lens unit in an optical axis direction during
zooming from the wide-angle end to the telephoto end, the amount of
movement m1 being positive when the first lens unit moves toward
the image side and negative when the first lens unit moves toward
the object side.
2. The zoom lens according to claim 1, wherein the following
condition is satisfied: 1.0<f3/fw<2.5 where f3 is a focal
length of the third lens unit.
3. The zoom lens according to claim 1, wherein the following
condition is satisfied: -2.2<m3/fw<-1.6 where m3 is an amount
of movement of the third lens unit in the optical axis direction
during zooming from the wide-angle end to the telephoto end, the
amount of movement m3 being positive when the third lens unit moves
toward the image side and negative when the third lens unit moves
toward the object side.
4. The zoom lens according to claim 1, wherein the following
condition is satisfied: 1.5<f2/f3<-0.8 where f2 and f3 are
focal lengths of the second lens unit and the third lens unit,
respectively.
5. The zoom lens according to claim 1, wherein the following
condition is satisfied: 1.0<(1-.beta.3T)-.beta.4T<3.0 where
.beta.3T and .beta.4T are lateral magnifications of the third lens
unit and the fourth lens unit, respectively, at the telephoto
end.
6. The zoom lens according to claim 1, wherein the following
condition is satisfied: 1.0<(1-.beta.3T)/(1-.beta.3W)<2.0
where .beta.3w and .beta.3T are lateral magnifications of the third
lens unit at the wide-angle end and the telephoto end,
respectively.
7. The zoom lens according to claim 1, wherein the negative lens
included in the second lens unit has an aspheric surface, and
wherein the following condition is satisfied: (N2P+N2N)/2>1.85
where N2N and N2P are refractive indices of materials of the
negative lens and the positive lens, respectively, which are
included in the second lens unit.
8. The zoom lens according to claim 1, wherein the third lens unit
includes at least one cemented lens including a positive lens and a
negative lens, and wherein the following condition is satisfied:
18<.nu.3P-.nu.3N<24 where .nu.3P and .nu.3N are Abbe numbers
of materials of the positive lens and the negative lens,
respectively, which form the cemented lens.
9. The zoom lens according to claim 1, wherein the fourth lens unit
moves in a direction from the object side toward the image side to
perform focusing from an object at infinity to a close object.
10. An image pickup apparatus, comprising: the zoom lens according
to claim 1; and a solid-state image pickup device that receives an
image formed by the zoom lens.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to zoom lenses suitable for
use in image pickup apparatuses such as still cameras, video
cameras, broadcasting cameras, and digital still cameras.
[0003] 2. Description of the Related Art
[0004] Recently, image pickup apparatuses (cameras), such as video
cameras and digital still cameras, including solid-state image
pickup devices have become smaller with increased
functionality.
[0005] Accordingly, demand has increased for small, high-zoom-ratio
zoom lenses having a small length and high optical performance over
the entire zoom range for use in image-forming optical systems of
the image pickup apparatuses.
[0006] In a retractable zoom lens having lens units that can be
retracted when the camera is not used, it is necessary to reduce
the number of lenses included in each lens unit and to reduce the
size of each lens unit in order to reduce the overall size of the
zoom lens.
[0007] In general, the size of the zoom lens can be reduced by
reducing the amount of movement of each lens unit during zooming
while increasing the refractive power of each lens unit, and
reducing the number of lenses included in each lens unit.
[0008] However, in the case in which the refractive power of each
lens unit in the zoom lens is increased, aberration variation
during zooming is also increased. Therefore, it becomes difficult
to obtain high optical performance over the entire zoom range and
over the entire image plane.
[0009] Therefore, to obtain a high zoom ratio and high optical
performance while reducing the size of the entire lens system, it
is important to adequately set the refractive power of each lens
unit and conditions under which each lens unit is moved during
zooming.
[0010] As an example of a small zoom lens having a zoom ratio of
4.5 or more, a zoom lens which includes four lens units and which
performs zooming by moving the lens units is described in U.S. Pat.
No. 6,853,496, U.S. Pat. No. 7,286,298, and U.S. Pat. No.
7,193,790. The zoom lens includes a lens unit having a positive
refractive power, a lens unit having a negative refractive power, a
lens unit having a positive refractive power, and a lens unit
having a positive refractive power arranged in that order from an
object side to an image side.
[0011] In the zoom lens including four lens units, the second lens
unit can be composed of a negative lens and a positive lens to
reduce the size of the entire system, as described in U.S. Pat. No.
5,134,524 and U.S. Pat. No. 6,577,450.
[0012] In this type of zoom lens including four lens units, the
high zoom ratio and high optical performance cannot be obtained
unless the lens structure of the first lens unit, the amount of
movement of the first lens unit during zooming, and the lens
structure of the second lens unit, which provides a
magnification-varying function, are adequately set.
SUMMARY OF THE INVENTION
[0013] The present invention is directed to a small,
high-zoom-ratio zoom lens capable of providing high optical
performance over the entire zoom range and an image pickup
apparatus including the zoom lens.
[0014] According to an embodiment of the present invention, a zoom
lens includes a first lens unit having a positive refractive power;
a second lens unit having a negative refractive power; a third lens
unit having a positive refractive power; and a fourth lens unit
having a positive refractive power. The first lens unit, the second
lens unit, the third lens unit, and the fourth lens unit are
arranged in that order from an object side to an image side. The
zoom lens performs zooming by changing distances between the lens
units. The first lens unit includes two or less lenses and the
second lens unit consists of a negative lens and a positive lens in
that order from the object side to the image side. The zoom lens
satisfies the following condition:
-1.3<m1/ {square root over ((fwfT))}<-0.8
where fw and fT are focal lengths of the entire lens system at a
wide-angle end and a telephoto end, respectively, and m1 is an
amount of movement of the first lens unit in an optical axis
direction during zooming from the wide-angle end to the telephoto
end, the amount of movement m1 being positive when the first lens
unit moves toward the image side and negative when the first lens
unit moves toward the object side.
[0015] Further features of the present invention will become
apparent from the following description of exemplary embodiments
with reference to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 illustrates a sectional view of a zoom lens according
to a first embodiment at a wide-angle end.
[0017] FIG. 2A illustrates aberration diagrams of the zoom lens
according to the first embodiment at a wide-angle end.
[0018] FIG. 2B illustrates aberration diagrams of the zoom lens
according to the first embodiment at a middle zoom position.
[0019] FIG. 2C illustrates aberration diagrams of the zoom lens
according to the first embodiment at a telephoto end.
[0020] FIG. 3 illustrates a sectional view of a zoom lens according
to a second embodiment at a wide-angle end.
[0021] FIG. 4A illustrates aberration diagrams of the zoom lens
according to the second embodiment at a wide-angle end.
[0022] FIG. 4B illustrates aberration diagrams of the zoom lens
according to the second embodiment at a middle zoom position.
[0023] FIG. 4C illustrates aberration diagrams of the zoom lens
according to the second embodiment at a telephoto end.
[0024] FIG. 5 illustrates a sectional view of a zoom lens according
to a third embodiment at a wide-angle end.
[0025] FIG. 6A illustrates aberration diagrams of the zoom lens
according to the third embodiment at a wide-angle end.
[0026] FIG. 6B illustrates aberration diagrams of the zoom lens
according to the third embodiment at a middle zoom position.
[0027] FIG. 6C illustrates aberration diagrams of the zoom lens
according to the third embodiment at a telephoto end.
[0028] FIG. 7 illustrates a sectional view of a zoom lens according
to a fourth embodiment at a wide-angle end.
[0029] FIG. 8A illustrates aberration diagrams of the zoom lens
according to the fourth embodiment at a wide-angle end.
[0030] FIG. 8B illustrates aberration diagrams of the zoom lens
according to the fourth embodiment at a middle zoom position.
[0031] FIG. 8C illustrates aberration diagrams of the zoom lens
according to the fourth embodiment at a telephoto end.
[0032] FIG. 9 illustrates a schematic diagram showing the major
part of an image pickup apparatus.
[0033] FIG. 10 illustrates a schematic diagram showing an F-number
stop.
DESCRIPTION OF THE EMBODIMENTS
[0034] Zoom lenses according to embodiments of the present
invention and an image pickup apparatus including any one of the
zoom lenses according to the embodiments will now be described.
[0035] Each of the zoom lenses according to the embodiments
includes a first lens unit having a positive refractive power, a
second lens unit having a negative refractive power, a third lens
unit having a positive refractive power, and a fourth lens unit
having a positive refractive power in that order from the object
side to the image side. The zoom lenses perform zooming by changing
the distances between the lens units.
[0036] FIG. 1 illustrates a sectional view of a zoom lens according
to a first embodiment of the present invention at a wide-angle end
(short-focal-length end).
[0037] FIGS. 2A, 2B, and 2C are aberration diagrams of the zoom
lens according to the first embodiment at a wide-angle end, a
middle zoom position, and a telephoto end (long-focal-length end),
respectively.
[0038] The zoom lens according to the first embodiment has a zoom
ratio of 4.85 and an F number of 2.63 to 4.96.
[0039] FIG. 3 illustrates a sectional view of a zoom lens according
to a second embodiment of the present invention at a wide-angle
end.
[0040] FIGS. 4A, 4B, and 4C are aberration diagrams of the zoom
lens according to the second embodiment at a wide-angle end, a
middle zoom position, and a telephoto end, respectively.
[0041] The zoom lens according to the second embodiment has a zoom
ratio of 4.84 and an F number of 2.64 to 5.41.
[0042] FIG. 5 illustrates a sectional view of a zoom lens according
to a third embodiment of the present invention at a wide-angle
end.
[0043] FIGS. 6A, 6B, and 6C are aberration diagrams of the zoom
lens according to the third embodiment at a wide-angle end, a
middle zoom position, and a telephoto end, respectively.
[0044] The zoom lens according to the third embodiment has a zoom
ratio of 4.81 and an F number of 2.88 to 4.84.
[0045] FIG. 7 illustrates a sectional view of a zoom lens according
to a fourth embodiment of the present invention at a wide-angle
end.
[0046] FIGS. 8A, 8B, and 8C are aberration diagrams of the zoom
lens according to the fourth embodiment at a wide-angle end, a
middle zoom position, and a telephoto end, respectively.
[0047] The zoom lens according to the fourth embodiment has a zoom
ratio of 4.85 and an F number of 2.88 to 4.90.
[0048] FIG. 9 is a schematic diagram showing the major part of an
image pickup apparatus including a zoom lens according to at least
one embodiment of the present invention.
[0049] The zoom lens according to each embodiment can be used as a
photographing lens system in an image pickup apparatus, such as a
digital still camera and a video camera.
[0050] In the sectional views of the zoom lenses, the object side
(front) is at the left and the image side (rear) is at the
right.
[0051] In the case in which the zoom lens according to each
embodiment is used as a projector lens in a projector or the like,
a screen is at the left and an image to be projected is at the
right.
[0052] Referring to the sectional views, each zoom lens includes a
first lens unit L1 having a positive refractive power (optical
power is the reciprocal of focal length), a second lens unit L2
having a negative refractive power, a third lens unit L3 having a
positive refractive power, and a fourth lens unit L4 having a
positive refractive power.
[0053] SP denotes an F-number stop (hereinafter referred to also as
an aperture stop) that determines (restricts) the full-aperture
F-number (Fno) rays. The aperture stop SP is on the object side of
the third lens unit L3 and moves together with or independently of
the third lens unit L3 during zooming.
[0054] G denotes an optical block corresponding to, for example, an
optical filter, a faceplate, a quartz low-pass filter, an
infrared-cut filter, etc.
[0055] IP denotes an image plane. When the zoom lens of each
embodiment is used as an image-forming optical system in a digital
still camera or a video camera, the image plane IP is placed on the
image pickup plane of a solid-state image pickup device
(photoelectric converter), such as a charged coupled device (CCD)
sensor and a complementary metal-oxide semiconductor (CMOS)
sensor.
[0056] When the zoom lens of each embodiment is used as an
image-forming optical system of a silver salt film camera, the
image plane IP corresponds to a film surface.
[0057] In the aberration diagrams, Fno indicates the F number, d
and g indicate the d-line and the g-line, respectively, and
.DELTA.M and .DELTA.S indicate a meridional image plane and a
sagittal image plane, respectively. The chromatic aberration of
magnification is shown by the g-line.
[0058] In each of the embodiments described below, the wide-angle
end and the telephoto end are zoom positions corresponding to the
states in which the lens unit having the magnification-varying
function is at one and the other ends of a moveable range on an
optical axis.
[0059] The refractive powers of the lens units will now be
described below.
[0060] Since the first lens unit L1 has a positive refractive
power, the spherical aberration and the axial chromatic aberration
can be easily corrected, in particular, at the telephoto end.
[0061] Since the second lens unit L2 has a negative refractive
power, image-plane variation due to field-angle characteristics can
be reduced. In addition, the field angle can be easily increased
and the overall size of the lens system can be easily reduced by
increasing the negative refractive power of the second lens unit
L2.
[0062] Since the third lens unit L3 has a positive refractive
power, the spherical aberration and the astigmatism can be
accurately corrected over the entire zoom range.
[0063] Since the fourth lens unit L4 has a positive refractive
power, high telecentricity can be provided at the image side. The
fourth lens unit L4 provides a function as a field lens. Therefore,
the zoom lens of each embodiment can be easily used in image pickup
apparatuses including solid-state image pickup devices.
[0064] The movement of each lens unit during zooming will now be
explained.
[0065] In each embodiment, the lens units L1 to L4 are moved as
shown by the arrows during zooming from the wide-angle end to the
telephoto end. The movement of each lens unit will be described in
detail.
[0066] The first lens unit L1 moves along a locus that is convex
toward the image side. The position of the first lens unit L1 at
the telephoto end is closer to the object side than that at the
wide-angle end.
[0067] In general, in the case of determining the front lens
diameter by off-axis rays at the wide-angle end, the front lens
diameter is determined by the field angle. More specifically, the
front lens diameter is increased as the field angle is increased.
In comparison, in the case of determining the front lens diameter
by the rays at the telephoto end, the front lens diameter is
determined by the Fno rays at the telephoto end. More specifically,
the front lens diameter is increased as the F number (Fno) at the
telephoto end is reduced.
[0068] In each embodiment, the amount of movement of the first lens
unit L1 during zooming is set to an adequate value so that the
front lens diameter is determined at the telephoto end. The F
number (Fno) at the telephoto end is reduced within such a range
that no damage is caused in a photographing operation, and
variation in Fno is set to an adequate range so that the diameter
can be increased at the wide-angle end.
[0069] The amount of movement of the first lens unit L1 during
zooming can be set so as to satisfy the conditional expression (1)
given below. Thus, the magnification-varying function obtained by
the first lens unit L1 and the second lens unit L2 can be improved
and the zoom ratio can be easily increased.
[0070] The second lens unit L2 moves along a locus that is convex
toward the image side. The position of the second lens unit L2 at
the telephoto end is closer to the image side than that at the
wide-angle end.
[0071] The third lens unit L3 is moved continuously toward the
object side. In each embodiment, the third lens unit L3 provides
the magnification-varying function together with the second lens
unit L2. The amount of movement of the third lens unit L3 can be
set so as to satisfy the conditional expression (3) given below. In
such a case, a high zoom ratio can be obtained.
[0072] In addition, variation in the lateral magnification of the
third lens unit L3 during zooming can be set so as to satisfy the
conditional expression (6) given below. Thus, variation in Fno
during zooming can be adequately set.
[0073] In general, Fno of an optical system is defined as
follows:
Fno=D/f A
where D is a diameter (pupil diameter) and f is a focal length of
the entire optical system.
[0074] In each embodiment, the zoom lens includes lens units having
a positive refractive power, a negative refractive power, a
positive refractive power, and a positive refractive power. The
aperture stop SP is positioned near the third lens unit L3. If the
position of the fourth lens unit L4 at the wide-angle end is
substantially the same as that at the telephoto end, the distance
between the third lens unit L3 and the image point of the third
lens unit L3 is substantially equivalent to the distance between
the aperture stop SP and the image plane.
[0075] If the pupil diameter is constant, Fno is increased
(brightness is reduced) as the distance between the aperture stop
SP and the image plane is increased. In other words, variation in
Fno is increased as the amount of movement of the third lens unit
L3 is increased.
[0076] The above-described relationship will be explained using
equations. First, the distance between the third lens unit L3 and
the image point of the third lens unit L3 can be expressed as
follows:
S3=(1-.beta.3T)f3 (B)
where .beta.3T is the lateral magnification of the third lens unit
L3 at the telephoto end, f3 is the focal length of the third lens
unit L3, and S3 is the distance between the principal point of the
third lens unit L3 and the image point of the third lens unit L3.
Variation in Fno can be expressed using equation (B) as
follows:
.DELTA.Fno={(1-.beta.3T)f3}/{(1-.beta.3W)f3} (C)
where .beta.3w is the lateral magnification of the third lens unit
L3 at the wide-angle end.
[0077] When FnoW and FnoT are F numbers at the wide-angle end and
the telephoto end, respectively, .DELTA.Fno can be expressed as
follows:
.DELTA.Fno.apprxeq.FnoT/Fnow (D)
[0078] In each embodiment, the amount of movement of the third lens
unit can be set so as to satisfy the conditional expression (3)
given below, so that Fno at the telephoto end can be reduced within
such a range that no damage is caused in the photographing
operation. Thus, variation in Fno during zooming is set to an
adequate level so as to increase the diameter at the wide-angle
end.
[0079] The fourth lens unit L4 moves along a locus that is convex
toward the object side.
[0080] With regard to the distances between the lens units, the
distance between the first lens unit L1 and the second lens unit L2
at the telephoto end is larger than that at the wide-angle end. The
distance between the second lens unit L2 and the third lens unit L3
at the telephoto end is smaller than that at the wide-angle end.
The distance between the third lens unit L3 and the fourth lens
unit L4 at the telephoto end is larger than that at the wide-angle
end.
[0081] In each embodiment, during zooming from the wide-angle end
to the telephoto end, the magnification-varying function is
obtained by moving the third lens unit L3 and the second lens unit
L2 independently of each other.
[0082] In each embodiment, the magnification-varying function is
mainly provided by the movement of the third lens unit L3 toward
the object side. The magnification-varying function is also
obtained by the movement of the second lens unit L2 along a locus
that is convex toward the image side.
[0083] In each embodiment, the refractive powers and the
arrangement of the lens units are set such that a refractive-power
distribution of a substantially retrofocus type can be obtained as
a whole at the wide-angle end.
[0084] In addition, the refractive powers and the arrangement of
the lens units are set such that a refractive-power distribution of
a substantially telephoto type can be obtained as a whole at the
telephoto end. As a result, a zoom lens with a high zoom ratio can
be obtained.
[0085] The zooming operation and correction of the image-plane
variation caused by the variation in magnification are performed by
moving all of the lens units. Therefore, efficient distribution of
the refractive powers can be easily provided.
[0086] In addition, the overall length of the optical system at the
wide-angle end is reduced so that a small, high-zoom-ratio zoom
lens that is suitable for use in, for example, a digital camera can
be obtained.
[0087] In each embodiment, a rear-focus method is used in which
focusing is performed by moving the fourth lens unit L4 along the
optical axis.
[0088] Focusing from an object at infinity to a close object at the
telephoto end can be performed by moving the fourth lens unit
forward, as shown by the arrow 4c.
[0089] The solid curve 4a represents a locus of the fourth lens
unit L4 for correcting the image-plane variation during zooming
from the wide-angle end to the telephoto end while an object at
infinity is in focus. The dashed curve 4b represents a locus of the
fourth lens unit L4 for correcting the image-plane variation during
zooming from the wide-angle end to the telephoto end while a close
object is in focus.
[0090] In each embodiment, focusing can be quickly performed
because the fourth lens unit L4, which is structured to be light,
is moved for focusing.
[0091] Although not described in the embodiments, the first lens
unit L1 can also be moved continuously toward the object side and
the second lens unit L2 can also be moved continuously toward the
image side during zooming from the wide-angle end to the telephoto
end. Also in such a case, the above-described effects can be
obtained.
[0092] In each embodiment, the third lens unit L3 can be moved in a
direction having a component perpendicular to the optical axis so
as to prevent the image blur when the entire optical system
vibrates.
[0093] Thus, an image stabilizing function can be obtained without
using an additional optical element, such as a variable angle
prism, or a lens unit dedicated to the image stabilizing function.
Consequently, the size of the entire optical system is prevented
from being increased.
[0094] In each embodiment, the zoom lens includes four lens units.
However, a lens unit having a refractive power or a converter lens
unit can be placed on the object side of the first lens unit L1 or
the image side of the fourth lens unit L4 as necessary.
[0095] Characteristics of the lens structure of each lens unit
included in the zoom lens of each embodiment will now be
described.
[0096] In each embodiment, the lens units include lens elements
described below in order from the object side to the image
side.
[0097] First, first to third embodiments will be described.
[0098] In the first to third embodiments, the lens units include
lens elements described below in order from the object side to the
image side.
[0099] The first lens unit L1 includes a cemented lens of a
negative lens and a positive lens. The cemented lens has a meniscus
shape and is convex on the object side.
[0100] The number of lenses included in the first lens unit L1 is
two or less.
[0101] The second lens unit L2 consists of a negative lens having a
concave surface on the image side and a positive lens having a
convex surface on the object side. The negative lens has aspheric
surfaces on both sides thereof.
[0102] The third lens unit L3 includes a biconvex positive lens and
a cemented lens of a positive lens and a negative lens. The
cemented lens has a meniscus shape and is convex on the object
side.
[0103] The fourth lens unit L4 includes a single biconvex positive
lens or a single positive lens having a meniscus shape with a
convex surface on the object side.
[0104] Thus, in the first to third embodiments, eight lenses are
used in total and high optical performance is provided while the
overall size of the optical system is reduced.
[0105] Characteristics of the lens structures of the lens units
included in the zoom lenses according to the first to third
embodiments will not be described.
[0106] In the zoom lenses according to the first to third
embodiments, the first lens unit L1 having a positive refractive
power has the largest effective diameter. Since the first lens unit
L1 includes the cemented lens, the thickness of the first lens unit
L1 is reduced and the height at which the off-axis rays are
incident on the first lens unit L1 at the wide-angle end can be
reduced. As a result, the size of the first lens unit L1 is
reduced.
[0107] In addition, since the first lens unit L1 includes two
lenses, which are a positive lens and a negative lens, the
chromatic aberration of magnification can be accurately corrected
during zooming from the wide-angle end to the telephoto end. In
addition, the axial chromatic aberration can be accurately
corrected at the telephoto end.
[0108] The second lens unit L2 is configured to have a high
negative refractive power to reduce the front lens diameter. In the
first to third embodiments, the number of lenses included in the
second lens unit L2 is two. Therefore, compared to the structure in
which the second lens unit L2 consists of a single lens, the
aberrations can be more accurately corrected while the high
refractive power is maintained.
[0109] In addition, compared to the structure in which the second
lens unit L2 consists of three lenses, the lens structure is made
simpler while the high zoom ratio is maintained by forming the
lenses included in the second lens unit L2 with a
high-refractive-index glass material.
[0110] The second lens unit L2 having a negative refractive power
provides the magnification-varying function together with the third
lens unit L3. In the first to third embodiments, the refractive
powers of the second lens unit L2 and the third lens unit L3 can be
set so as to satisfy the conditional expression (4) given below. In
such a case, the front lens diameter can be reduced while a high
zoom ratio is ensured.
[0111] The negative lens included in the second lens unit L2 has at
least one aspheric surface. More specifically, the negative lens
has aspheric surfaces on both sides thereof. Therefore, aberration
variation during zooming can be accurately corrected.
[0112] The third lens unit L3 having a positive refractive power is
disposed near the aperture stop SP. The third lens unit L3 causes
large spherical aberration and axial aberrations, such as the axial
chromatic aberration, over the entire zoom range.
[0113] Therefore, in the first to third embodiments, the refractive
power of the third lens unit L3 is set so as to satisfy the
conditional expression (2) given below, so that high optical
performance can be obtained.
[0114] The positive refractive power of the third lens unit L3 is
obtained by two lenses, so that the spherical aberration can be
accurately corrected. The axial chromatic aberration caused by the
positive lens is corrected by the negative lens. Due to this lens
structure, high optical performance can be obtained by a small
number of lenses.
[0115] In the zoom lens according to each of the first to third
embodiments, to accurately correct the optical performance in the
image stabilizing operation, the lateral magnification of the third
lens unit L3, which is a shift lens unit, and the lateral
magnification of the fourth lens unit L4, which is disposed behind
the third lens unit L3, are set so as to satisfy the conditional
expression (5) given below. In general, the amount of movement A of
the image point on the image plane caused when a shift lens unit A
is shifted by 1 mm can be expressed as follows:
.DELTA.=(1-.beta.A).beta.B (E)
where .DELTA. is the amount of movement of the image point on the
image plane, .beta.A is the lateral magnification of the shift lens
unit, and .beta.B is the lateral magnification of the lens unit
disposed behind the shift lens unit.
[0116] In the zoom lens according to each of the first to third
embodiments, the image stabilizing operation (correction of image
blur) is performed by shifting the third lens unit L3. In other
words, the third lens unit L3 functions as the shift lens unit and
the fourth lens unit L4 functions as the lens unit disposed behind
the shift lens unit.
[0117] In the first to third embodiments, the lateral
magnifications of the third lens unit L3 and the fourth lens unit
L4 are set such that the amount of movement A in equation (E) can
be set to an adequate value.
[0118] The third lens unit L3 includes one or more aspheric
surfaces, so that aberration variation during zooming can be
accurately corrected.
[0119] FIG. 10 illustrates the arrangement of an F-number stop SP
provided on the third lens unit L3.
[0120] As shown in FIG. 10, the F-number stop SP is positioned
between a vertex G31a of an object-side surface R9 of a lens G31
and an intersecting point G31b of the object-side surface R9 and a
peripheral portion (edge portion) P5 of the lens G31 in the
direction of the optical axis. The lens G31 is closest to the
object side in the third lens unit L3.
[0121] Thus, the F-number stop SP is disposed in the third lens
unit L3 and is moved together with the third lens unit L3 during
zooming, so that the distance between the entrance pupil and the
second lens unit L2 is reduced in the wide-angle region.
[0122] When the aperture stop SP is disposed as described above,
the distance between the second lens unit L2 and the third lens
unit L3 can be reduced at the telephoto end. Therefore, the
distance by which the third lens unit L3 can be moved toward the
object side during zooming is ensured, and the zoom ratio can be
increased without increasing the overall length of the lens system
at the telephoto end.
[0123] The fourth lens unit L4 having a positive refractive power
efficiently corrects off-axis aberrations and the axial aberrations
that cannot be sufficiently corrected by the third lens unit
L3.
[0124] The fourth lens unit L4 has an aspheric surface on the
object side so that aberration variation can be reduced during
focusing.
[0125] The lens structure of each lens unit in the fourth
embodiment will now be described.
[0126] In the fourth embodiment, the lens structures of the first
lens unit L1 and the fourth lens unit L4 are different from those
in the first to third embodiments. The structures of the other lens
units are similar to those in the first to third embodiments.
[0127] In the fourth embodiment, the lens units include lens
elements described below in order from the object side to the image
side.
[0128] The first lens unit L1 includes a single positive lens. The
positive lens has a meniscus shape and is convex on the object
side.
[0129] The second lens unit L2 consists of a biconcave negative
lens and a positive lens having a convex surface on the object
side. The negative lens has aspheric surfaces on both sides
thereof.
[0130] The third lens unit L3 includes a biconvex positive lens and
a cemented lens of a positive lens and a negative lens. The
cemented lens has a meniscus shape and is convex on the object
side.
[0131] The fourth lens unit L4 includes a cemented lens of a
positive lens and a negative lens. The cemented lens has a meniscus
shape and is convex on the object side.
[0132] In the fourth embodiment, eight lenses are used in total and
high optical performance is provided while the overall size of the
optical system is reduced.
[0133] In the zoom lens according to the fourth embodiment, the
first lens unit L1 having a positive refractive power has the
largest effective diameter. The first lens unit L1 includes a
single lens so that the overall size of the optical system is
reduced.
[0134] The positive lens included in the first lens unit L1 is made
of a low-dispersion material, so that the axial chromatic
aberration can be accurately corrected, in particular, at the
telephoto end.
[0135] Characteristics of the lens structures of the second lens
unit L2 and the third lens unit L3 are similar to those of the
first to third embodiments.
[0136] The fourth lens unit L4 having a positive refractive power
efficiently corrects the off-axis aberrations and the axial
aberrations that cannot be sufficiently corrected by the third lens
unit L3. In addition, in the fourth embodiment, the chromatic
aberration of magnification that cannot be sufficiently corrected
by the first lens unit L1 including a single positive lens is
corrected, in particular, at the telephoto end, by the positive
lens and the negative lens included in the fourth lens unit L4.
[0137] As described above, although the zoom lens according to each
of the above-described embodiments includes eight lenses and the
overall length of the lens system is reduced, high optical
performance with a zoom ratio of 4.5 or more and high brightness
can be obtained.
[0138] In the zoom lens according to each of the embodiments, to
further improve the optical performance or to further reduce the
overall size of the lens system, one or more of the conditional
expressions given below can be satisfied. In such a case, effects
corresponding to the conditional expressions can be obtained.
[0139] In the conditional expressions, the focal lengths of the
entire lens system at the wide-angle end and the telephoto end are
indicated by fw and fT, respectively.
[0140] The amounts of movement of the first lens unit L1 and the
third lens unit L3 in the optical-axis direction during zooming
from the wide-angle end to the telephoto end are indicated by m1
and m3, respectively. With regard to the sign of the amount of
movement, the positive sign represents the movement toward the
image side, and the negative sign represents the movement toward
the object side.
[0141] If the movement is a reciprocating movement, the position at
the wide-angle end is used as a reference and the difference
between the position at the wide-angle end and the position at the
telephoto end is determined as the amount of movement.
[0142] The focal lengths of the second lens unit L2 and the third
lens unit L3 are indicated by f2 and f3, respectively.
[0143] The lateral magnifications of the third lens unit L3 at the
wide-angle end and the telephoto end are indicated by .beta.3w and
.beta.3T, respectively.
[0144] The lateral magnification of the fourth lens unit L4 at the
telephoto end is indicated by .beta.4T.
[0145] The refractive indices of the materials of the negative lens
and the positive lens included in the second lens unit L2 are
indicated by N2N and N2P, respectively.
[0146] The Abbe numbers of the materials of the positive lens and
the negative lens forming the cemented lens included in the third
lens unit L3 are indicated by .nu.3P and 84 3N, respectively.
[0147] The conditional expressions are as follows:
1.3<m1/ {square root over ((fwfT))}<-0.8 (1)
1.0<f3/fw<2.5 (2)
-2.2<m3/fw<-1.6 (3)
-1.5<f2/f3<-0.8 (4)
1.0<(1-.beta.3T)-.beta.4T<3.0 (5)
1.0<(1.beta.3T)/(1-.beta.3W)<2.0 (6)
(N2P+N2N)/2>1.85 (7)
18<.nu.3P-.nu.3N<24 (8)
[0148] The technical meaning of each conditional expression will
now be described.
[0149] Conditional expression (1) represents the condition for
adequately setting the amount of movement of the first lens unit L1
during zooming and accurately correcting the aberration variation
during zooming when the front lens diameter is reduced and a zoom
ratio of 4.5 or more is obtained.
[0150] If the amount of movement m1 of the first lens unit L1 is
small and the value of conditional expression (1) is above the
higher limit thereof, the magnification-varying function obtained
by the first lens unit L1 and the second lens unit L2 is small.
[0151] In such a case, the amount of movement of the third lens
unit L3 must be increased to obtain a desired zoom ratio. However,
the distance between the second lens unit L2 and the third lens
unit L3 at the wide-angle end must be increased to prevent the
third lens unit L3 from interfering with the second lens unit L2.
Consequently, the overall length of the lens system is increased at
the wide-angle end.
[0152] If the amount of movement m1 of the first lens unit L1 is
large and the value of conditional expression (1) is below the
lower limit thereof, the overall length of the lens system is
increased at the telephoto end. As a result, when the zoom lens has
a retractable structure in which the lens units can be retracted,
the number of retracting units is increased and the lens barrel
structure becomes complex.
[0153] The value of conditional expression (2) is obtained by
normalizing the focal length of the third lens unit L3 with the
focal length fw of the entire system at the wide-angle end.
[0154] If the focal length of the third lens unit L3 is increased
such that the value of conditional expression (2) is above the
upper limit thereof, that is, if the refractive power of the third
lens unit L3 is too low, aberration variation during zooming is
reduced. However, the amount of movement of the third lens unit L3
during zooming is increased and the overall length of the lens
system is increased at the telephoto end.
[0155] If the focal length of the third lens unit L3 is reduced
such that the value of conditional expression (2) is below the
lower limit thereof, that is, if the refractive power of the third
lens unit L3 is too high, it becomes difficult to correct the
spherical aberration in the entire zoom range and the chromatic
spherical aberration at the telephoto end.
[0156] The value of conditional expression (3) is obtained by
normalizing the amount of movement m3 of the third lens unit L3
during zooming with the focal length fw of the entire system at the
wide-angle end.
[0157] If the amount of movement m3 of the third lens unit L3 is
increased such that the value of conditional expression (3) is
above the upper limit, the amount of movement of the first lens
unit L1 for correcting the image-plane variation during zooming is
increased. As a result, the overall length of the lens system is
increased at the telephoto end and the front lens diameter is
increased accordingly.
[0158] If the amount of movement m3 of the third lens unit L3 is
reduced such that the value of conditional expression (3) is below
the lower limit, variation in Fno during zooming is reduced.
Therefore, the diameter cannot be increased at the wide-angle
end.
[0159] The value of conditional expression (4) is obtained by
normalizing the focal length of the second lens unit L2 with the
focal length of the third lens unit L3. If the focal length of the
second lens unit L2 is increased such that the value of conditional
expression (4) is above the upper limit thereof, that is, if the
refractive power of the second lens unit L2 is too low, it becomes
difficult to correct the chromatic aberration of magnification
during zooming.
[0160] If the focal length of the second lens unit L2 is reduced
such that the value of conditional expression (4) is below the
lower limit thereof, that is, if the refractive power of the second
lens unit L2 is too high, the Petzval sum is increased in a
negative direction. Therefore, the image plane is excessively
corrected, in particular, at the wide-angle end. To prevent this,
the refractive power must be provided by two or more lenses and the
number of lenses included in the second lens unit L2 must be
increased.
[0161] Conditional expression (5) relates to sensitivity to
eccentricity of the third lens unit L3. If the value of conditional
expression (5) is above the upper limit thereof, the sensitivity to
eccentricity is too high. Therefore, although the amount of
movement of the shift lens unit (third lens unit L3) required in
the image stabilizing operation can be reduced, mechanical control
for adequately performing the image stabilizing operation becomes
difficult.
[0162] If the value of conditional expression (5) is below the
lower limit thereof, the sensitivity to eccentricity is too low.
Therefore, although the mechanical control for the image
stabilizing operation can be simplified, the amount of movement of
the shift lens unit required in the image stabilizing operation is
increased. As a result, the optical performance is largely degraded
due to the image stabilizing operation.
[0163] Conditional expression (6) relates to variation in F number
(Fno) during zooming.
[0164] If the value of conditional expression (6) is above the
upper limit thereof, variation in Fno during zooming is too large
and Fno becomes lower than a desired value at the wide-angle end.
As a result, it becomes difficult to correct the spherical
aberration and the coma aberration at the wide-angle end.
[0165] If the value of conditional expression (6) is below the
lower limit thereof, variation in Fno during zooming is too small
and the diameter cannot be increased at the wide-angle end.
[0166] Conditional expression (7) relates to the average refractive
index of the lenses included in the second lens unit L2.
[0167] If the average refractive index is below the lower limit of
conditional expression (7), the curvature of the surface of each
lens is increased. Therefore, the uneven thickness ratio of the
negative lens is increased and the lens volume is increased
accordingly. In addition, the on-axis lens thickness of the
positive lens is increased to ensure the edge thickness thereof,
and therefore the size of the second lens unit L2 is increased. In
addition, if the average refractive index is below the lower limit
of conditional expression (7), the volume of the second lens unit
L2 is increased, and the overall length of the lens system is
increased accordingly.
[0168] Conditional expression (8) relates to the difference in the
Abbe number between the materials of the positive lens and the
negative lens forming the cemented lens in the third lens unit
L3.
[0169] If the difference in the Abbe number is larger than the
upper limit of conditional expression (8), the axial chromatic
aberration is excessively corrected, in particular, at the
telephoto end.
[0170] If the difference in the Abbe number is smaller than the
lower limit of conditional expression (8), the chromatic spherical
aberration cannot be sufficiently corrected, in particular, at the
telephoto end.
[0171] In each of the above-described embodiments, the numerical
ranges of conditional expression (1) to (8) can also be set as
follows:
- 1 2 < m 1 / ( fw fT ) < - 0 9 ( 1 a ) ##EQU00001##
1.6<f3/fw<1.9 (2a)
-2.1<m3/fw<-1.6 (3a)
-1.0<f2/f3<-0.8 (4a)
1.3<(1-.beta.3T).beta.4T<2.0 (5a)
1.3<(1-.beta.3T)/(1.beta.3W)<1.8 (6a)
(N2P+N2N)/2>1.88 (7a)
20<.nu.3P-.nu.3N<22 (8a)
[0172] As described above, according to each of the above-described
embodiments, the lens structure of each lens unit, the positions of
aspheric surfaces, the method of moving each lens unit during
zooming, etc., are adequately determined. Thus, a zoom lens is
provided which includes a small number of lenses so that the
overall length thereof can be reduced, which is capable of
providing high optical performance with a zoom ratio of 4.5 or more
and small Fno, and which is suitable for use in, for example, a
digital still camera.
[0173] Numerical examples according to the present invention will
now be described. In each numerical example, indicates the surface
number counted from the object side, Ri indicates the radius of
curvature of the i.sup.th lens surface (i.sup.th surface), Di
indicates the distance between the i.sup.th and (i+1).sup.th lens
surfaces, and Ni and .nu.i indicate the refractive index and the
Abbe number, respectively, based on the d-line.
[0174] Two surfaces closest to the image side are surfaces forming
a filter member, such as a quartz low-pass filter, an infrared-cut
filter, etc.
[0175] When X is the displacement from the vertex of an aspheric
surface in the optical-axis direction at a height of h from the
optical axis, the shape of the aspheric surface is expressed as
follows:
X=(h.sup.2/R)/[1+{1-(1+k)(h/R).sup.2}.sup.1/2]Ah.sup.2+Bh.sup.4+Ch.sup.6-
+Dh.sup.8+Eh.sup.10Fh.sup.12
where k is the conic constant, A, B, C, D, and E are the aspherical
coefficients for the second, fourth, sixth, eight, tenth, and
twelfth orders, respectively, and R is the paraxial radius of
curvature.
[0176] In addition, "e-0X" indicates ".times.10.sup.-x." In
addition, f is the focal length, Fno is the F number, and .omega.
is the half field angle.
[0177] Table 1 provided below shows the values of the
above-described conditional expressions in each numerical
example.
[0178] The values of D8 in the first to third numerical examples
and the value of D7 in the fourth numerical example are negative
since the F-number stop and the lens G31 in the third lens unit L3
are counted in that order from the object side.
[0179] More specifically, the F-number stop (aperture stop) SP is
closer to the image side than the vertex G31a of the object-side
surface R9 (or R8) of the lens G31 positioned closest to the object
side in the third lens unit L3 by a distance corresponding to the
absolute value of D8 (or D7).
First Numerical Example
TABLE-US-00001 [0180] f = 6.58~31.89 Fno = 2.63~4.96 2.omega. =
60.5.degree.~13.7.degree. R1 = 18.156 D1 = 0.87 N1 = 1.84666 .nu.1
= 23.93 R2 = 13.919 D2 = 2.76 N2 = 1.62299 .nu.2 = 58.16 R3 =
72.157 D3 = Variable * R4 = 19895.562 D4 = 0.70 N4 = 1.85960 .nu.4
= 40.40 * R5 = 5.273 D5 = 2.48 R6 = 10.771 D6 = 1.71 N6 = 1.92286
.nu.6 = 18.90 R7 = 26.012 D7 = Variable R8 = Aperture D8 = -0.30 *
R9 = 5.591 D9 = 2.50 N9 = 1.51823 .nu.9 = 58.90 R10 = -13.388 D10 =
0 R11 = 5.522 D11 = 2.03 N11 = 1.74400 .nu.11 = 44.78 R12 = 52.417
D12 = 0.89 N12 = 1.84666 .nu.12 = 23.78 R13 = 3.636 D13 = Variable
* R14 = 8.090 D14 = 2.60 N14 = 1.58313 .nu.14 = 59.40 R15 = -53.744
D15 = Variable R16 = .infin. D16 = 0.72 N16 = 1.51633 .nu.16 =
64.14 R17 = .infin. Focal Length Variable Distance 6.58 15.91 31.89
D3 1.14 8.88 15.38 D7 11.50 2.07 0.78 D13 4.55 7.30 17.38 D15 3.20
5.82 2.26 Aspherical Coefficients 4th Surface K = -1.55114E+11 A =
-8.57773E-03 B = 1.96683E-05 C = 5.26031E-06 D = -6.22285E-08 E =
9.76602E-10 F = -4.03491E-11 5th Surface K = -3.68708E+00 A =
-2.22979E-03 B = 2.45160E-03 C = -7.87695E-05 D = 2.81346E-06 E =
-3.11063E-09 F = -1.50969E-09 9th Surface K = -1.26302E+00 A =
-2.90768E-02 B = -3.16506E-05 C = -6.33294E-06 D = 4.21168E-07 E =
-2.46592E-08 F = 1.82632E-09 14th Surface K = -2.98146E-01 A =
-1.33524E-02 B = -6.71518E-05 C = -3.48944E-07 D = -2.22719E-08 E =
7.60882E-09 F = -2.27799E-10
Second Numerical Example
TABLE-US-00002 [0181] f = 6.59~31.87 Fno = 2.64~5.41 2.omega. =
60.5.degree.~13.7.degree. R1 = 16.292 D1 = 0.87 N1 = 1.84666 .nu.1
= 23.93 R2 = 12.874 D2 = 2.50 N2 = 1.62299 .nu.2 = 58.16 R3 =
34.101 D3 = Variable * R4 = 24213.428 D4 = 0.70 N4 = 1.85960 .nu.4
= 40.40 * R5 = 5.290 D5 = 2.58 R6 = 10.918 D6 = 1.59 N6 = 1.92286
.nu.6 = 18.90 R7 = 25.415 D7 = Variable R8 = Aperture D8 = -0.30 *
R9 = 6.143 D9 = 2.88 N9 = 1.51823 .nu.9 = 58.90 R10 = -13.828 D10 =
0 R11 = 5.238 D11 = 1.95 N11 = 1.74400 .nu.11 = 44.78 R12 = 33.706
D12 = 0.86 N12 = 1.84666 .nu.12 = 23.78 R13 = 3.727 D13 = Variable
* R14 = 8.339 D14 = 2.76 N14 = 1.58313 .nu.14 = 59.40 R15 = 142.503
D15 = Variable R16 = .infin. D16 = 0.72 N16 = 1.51633 .nu.16 =
64.14 R17 = .infin. Focal Length Variable Distance 6.59 15.94 31.87
D3 1.06 10.11 17.45 D7 13.40 2.51 1.05 D13 4.77 8.13 19.41 D15 3.20
5.52 1.75 Aspherical Coefficients 4th Surface K = -1.55114E+11 A =
-1.70246E-03 B = 1.21945E-04 C = 1.49847E-06 D = -5.62598E-08 E =
9.94957E-10 F = -1.19636E-11 5th Surface K = -3.45531E+00 A =
-5.12588E-03 B = 2.46889E-03 C = -7.60693E-05 D = 3.12341E-06 E =
-6.58254E-08 F = 4.53055E-10 9th Surface K = -1.27815E+00 A =
-3.20280E-02 B = -2.15613E-05 C = -3.61988E-06 D = 6.10894E-07 E =
-6.13940E-08 F = 7.11943E-10 14th Surface K = -8.07022E-02 A =
-3.90466E-03 B = -1.10500E-04 C = 3.39318E-06 D = -1.08638E-07 E =
3.07644E-09 F = -4.19083E-11
Third Numerical Example
TABLE-US-00003 [0182] f = 6.58~31.65 Fno = 2.88~4.84 2.omega. =
60.6.degree.~13.8.degree. R1 = 17.446 D1 = 0.87 N1 = 1.84666 .nu.1
= 23.93 R2 = 13.487 D2 = 2.47 N2 = 1.69680 .nu.2 = 55.53 R3 =
39.058 D3 = Variable * R4 = -6037.659 D4 = 0.70 N4 = 1.85960 .nu.4
= 40.40 * R5 = 4.913 D5 = 2.03 R6 = 7.95 D6 = 1.90 N6 = 1.92286
.nu.6 = 18.90 R7 = 12.632 D7 = Variable R8 = Aperture D8 = -0.30 *
R9 = 8.051 D9 = 2.0 N9 = 1.51823 .nu.9 = 58.90 R10 = -15.46 D10 = 0
R11 = 4.763 D11 = 1.27 N11 = 1.74400 .nu.11 = 44.78 R12 = 10.422
D12 = 0.41 N12 = 1.84666 .nu.12 = 23.78 R13 = 3.924 D13 = Variable
* R14 = 6.706 D14 = 2.0 N14 = 1.62299 .nu.14 = 58.16 R15 = 32.811
D15 = Variable R16 = .infin. D16 = 0.72 N16 = 1.51633 .nu.16 =
64.14 R17 = .infin. Focal Length Variable Distance 6.58 15.00 31.65
D3 0.72 9.01 16.24 D7 17.14 6.31 2.38 D13 8.77 10.00 19.13 D15 3.15
6.40 5.29 Aspherical Coefficients 4th Surface K = -1.55114E+11 A =
1.06745E-02 B = -1.15013E-04 C = 2.08934E-06 D = -4.57323E-08 E =
1.32157E-09 F = -1.17922E-11 5th Surface K = -3.00904E+00 A =
2.17624E-03 B = 2.59865E-03 C = -7.76675E-05 D = 3.26179E-06 E =
-8.77024E-08 F = 1.27384E-09 9th Surface K = -8.36940E-01 A =
-1.75826E-04 B = -8.04904E-06 C = 1.20622E-06 D = -1.63321E-07 E =
7.24849E-09 F = 0.00000E+00 14th Surface K = -7.59824E-01 A =
-2.38772E-02 B = -1.10606E-04 C = 2.94734E-06 D = -1.59962E-07 E =
3.85088E-09 F = 0.00000E+00
Fourth Numerical Example
TABLE-US-00004 [0183] f = 6.58~31.89 Fno = 2.88~4.90 2.omega. =
60.5.degree.~13.7.degree. R1 = 21.336 D1 = 3.02 N1 = 1.51633 .nu.1
= 64.14 R2 = 303.173 D2 = Variable * R3 = -2090.826 D3 = 1.42 N3 =
1.88300 .nu.3 = 40.76 * R4 = 6.286 D4 = 2.01 R5 = 9.351 D5 = 2.0 N5
= 1.92286 .nu.5 = 18.90 R6 = 19.123 D6 = Variable R7 = Aperture D7
= -0.30 * R8 = 7.148 D8 = 2.50 N8 = 1.69350 .nu.8 = 53.21 R9 =
-28.612 D9 = 0.27 R10 = 7.585 D10 = 1.86 N10 = 1.69680 .nu.10 =
55.53 R11 = -20.366 D11 = 0.62 N11 = 1.84666 .nu.11 = 23.93 R12 =
4.072 D12 = Variable * R13 = -4.980 D13 = 2.63 N13 = 1.80486 .nu.13
= 24.74 R14 = -19.934 D14 = 0.71 N14 = 1.69680 .nu.14 = 55.53 R15 =
73.422 D15 = Variable R16 = .infin. D16 = 0.72 N16 = 1.51633 .nu.16
= 64.14 R17 = .infin. Focal Length Variable Distance 6.58 11.52
31.89 D2 0.49 6.49 17.35 D6 14.71 7.40 1.90 D12 2.34 3.67 14.49 D15
4.25 5.33 3.05 Aspherical Coefficients 3rd Surface K = -9.29016E+05
A = -3.93124E-03 B = 5.82504E-05 C = 2.06060E-06 D = -6.70513E-09 E
= -7.36062E-10 F = 7.67359E-12 4th Surface K = -1.81424E-01 A =
2.48639E-03 B = -3.99043E-05 C = 5.95228E-06 D = 1.06950E-08 E =
2.70297E-09 F = -1.67932E-10 8th Surface K = -1.48111E+00 A =
2.76751E-03 B = 1.66592E-04 C = -9.77407E-06 D = 1.13625E-06 E =
-8.76335E-08 F = 4.99308E-09 13th Surface K = -9.83818E-01 A =
1.44170E-01 B = 8.71054E-05 C = 1.74646E-06 D = -8.69182E-08 E =
1.86508E-09 F = 0.00000E+00
TABLE-US-00005 TABLE 1 1st Example 2nd Example 3rd Example 4th
Example Expression (1) -1.06 -1.19 -0.92 -1.04 Expression (2) 1.61
1.75 1.82 1.89 Expression (3) -1.81 -2.00 -1.90 -1.66 Expression
(4) -0.91 -0.96 -0.81 -0.91 Expression (5) 1.91 1.91 1.84 1.45
Expression (6) 1.57 1.59 1.75 1.37 Expression (7) 1.89 1.89 1.89
1.89 Expression (8) 21.0 21.00 21.00 21.0
[0184] Next, a digital still camera including the zoom lens
according to any one of the first to fourth embodiments as an
image-forming optical system will be described below with reference
to FIG. 9.
[0185] Referring to FIG. 9, the digital still camera includes a
camera body 20; an image-forming optical system 21 including the
zoom lens according to any one of the first to fourth embodiments;
a solid-state image pickup device (photoelectric converter) 22,
such as a CCD sensor and a CMOS sensor, that is mounted in the
camera body 20 and that receives an object image formed by the
image-forming optical system 21; a memory 23 that records
information corresponding to the object image obtained as a result
of photoelectric conversion performed by the solid-state
image-pickup device 22; and a finder 24 including a liquid crystal
display panel or other display and can be used to observe the
object image formed on the solid-state image pickup device 22.
[0186] Thus, a small, high-optical-performance image pickup
apparatus, such as a digital still camera, can be obtained by
applying a zoom lens according to an embodiment of the present
invention.
[0187] The zoom lens according to an embodiment of the present
invention can also be used in single-lens reflex cameras, video
cameras, etc.
[0188] While the present invention has been described with
reference to exemplary embodiments, it is to be understood that the
invention is not limited to the disclosed exemplary embodiments.
The scope of the following claims is to be accorded the broadest
interpretation so as to encompass all modifications and equivalent
structures and functions.
[0189] This application claims the benefit of Japanese Application
No. 2007-140256 filed May 28, 2007, which is hereby incorporated by
reference herein in its entirety.
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